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As perennials, poinsettias (Euphorbia pulcherrima) brighten late-season Mediterranean-climate gardens in U.S. Department of Agriculture plant hardiness zones 9 through 11. In colder areas, they've become staples of indoor winter decorating schemes. So a mysterious white substance and streams of ants covering your poinsettia's flame-red bracts and pine-green leaves are nothing if not alarming. The culprits responsible are messy, sap-stealing insects. Without quick treatment, they may doom your plant.

Meet the Mealybugs

As tender-stemmed plants, poinsettias are favorite feeding sites for pink hibiscus mealybugs. The pinkish insects conceal themselves beneath a protective coating of powdery white wax. Thanks to the wax and their fluffy white egg sacs, the mealybugs resemble bits of cotton fluff scattered over the poinsettia's stems and leaves. Adult mealybugs overwinter on poinsettia stems and leaves or in the soil around the plants. Their newly hatched larvae crawl from the egg sacs to start feeding. Wind and ants also carry them to new locations.

Detect the Damage

The mealybugs feed by sucking the sap stems and foliage. In the process, they also inject toxic, leaf-curling saliva. Twisted stems, stunted growth and failure to bloom all point to their presence, and a severely infested poinsettia may die. The insects have another annoying habit: They excrete undigested sap as sticky, transparent honeydew, a sugary waste that lures hungry ants to the infested plant.

Annihilate the Ants

Ants are voracious honeydew feeders, and you'll have them on your poinsettia as long as your plant has mealybugs. To control the ants, set sugar-based, boric-acid-laced ant stakes along the ant trails leading to your plant. When they come to collect the honeydew, some of the ants will also transport the bait back to their nests, where it will slowly poison the entire colony. It may be more than a month before your poinsettia is free of the ants.

Ax Them With Alcohol

While waiting for the ants to disappear, combine your baiting efforts with a direct attack on the mealybugs. Chemical insecticides don't penetrate the insects' wax covering. To do the job, spray your poinsettia until it drips with a solution of 1 quart of water, 1 cup of rubbing alcohol and 1 teaspoon of insecticidal soap concentrate. The alcohol dissolves the adult bugs' waxy coating so they die, and the insecticidal soap suffocates the larva and eggs. Repeat the application daily or every other day until the mealybugs are gone.

Wash Them Away

Pink hibiscus mealybugs are capable of reproducing several times a year. Once you've eliminated an infestation, monitor your poinsettia regularly. At the first sign of a new infestation, set your garden hose attachment on fine and direct the spray to the backs of the leaves and the stems. For maximum effectiveness, spray in the early morning for three consecutive days.

About the Author

Passionate for travel and the well-written word, Judy Wolfe is a professional writer with a Bachelor of Arts in English literature from Cal Poly Pomona and a certificate in advanced floral design. Her thousands of published articles cover topics from travel and gardening to pet care and technology.